This invention relates generally to computer communications through an interface defined by the standards of the Personal Computer Memory Card International Association (PCMCIA), which interface is hereinafter referred to as a PCMCIA interface. The invention more specifically relates to an apparatus and a method for communicating multiple devices, whether of the same or different operating features (i.e., protocols), with a personal computer through a single PCMCIA interface of the computer (i.e., the computer may have more than one PCMCIA interface, but the present invention connects to and communicates with only one of them in a given installation).
Physically small, microprocessor-based computers referred to as personal computers, workstations, laptop computers, notebook computers, pocket computers, etc. have physical limits defined by their respective housings or packaging. To communicate outside these physical limits, these computers have interfaces to which external devices can be connected. For example, personal computers typically have at least one serial port to which a serial interface device such as a modem, a mouse or a scanner can be connected. Personal computers also typically have at least one parallel port to which a parallel interface device such as a printer can be connected.
Such interfaces require circuitry that connects both with the external device and with the internal microprocessor circuitry. As with the various types of microprocessor-based computers, different interface circuits may be embodied in different physical sizes. Some of these interface circuits are too big for the smaller physical sizes of some of these computers. To accommodate these smaller-sized computers, the PCMCIA promulgated standards for an interface known as the PCMCIA input/output and memory card interface (the aforementioned "PCMCIA interface"). This 68-pin interface has only one interrupt request line, which is the communication path over which an external device can send an electrical signal to get the computer's attention.
Because of its single interrupt request line, each PCMCIA interface of a computer has been used with only one external device. To accommodate additional external devices, additional interfaces would be needed; however, this sometimes cannot be done because the computer housing is not large enough to receive additional PCMCIA interface circuits despite their relatively small size. Even if there were room for more PCMCIA interfaces to be installed, adding more interfaces would increase the cost. Thus, there is the need for an apparatus and method by which more than one external device can communicate through a single PCMCIA interface.